Daphnia exilis Herrick, 1895 (Crustacea: Cladocera): Una especie zooplanctónica potencialmente utilizable como organismo de prueba en bioensayos de toxicidad aguda en ambientes tropicales y subtropicales

the assessment of the toxic effects of chemical pollutants on the aquatic biota is fundamental for the accomplishment of control measures aimed to prevent and limit the pollution of aquatic ecosystems. zooplankters are frequently used as test organism in the aquatic toxicity evaluation, and the cladoceran daphnia magna is the main species globally used for this purpose, yet the convenience of use d. magna in tropical and subtropical regions has being discussed. nevertheless, the proposal of other surrogate species is restricted due to the lack of biological and toxicological information which justify and give support to these alternatives. daphnia exilis is a big cladoceran widely distributed in north america; in this study, a method for the controlled production of d. exilis neonates was tested. the sensitivity of this cladoceran was assessed with the reference toxicant hexavalent chromium (cr(vi)), at 20 and 25 °c. the 48-h median lethal concentration (lc50) was 0.1170 ± 0.0068 and 0.0802 ± 0.0057mg l-1, respectively at 20 y 25 °c; these values were lower than those reported for d. magna (0.2076 ± 0.0164 and 0.1544 ± 0.0175 mg l-1, at 20 y 25 °c respectively), thus indicating a higher sensitivity of d. exilis. considering its large size (both for adults and neonates), the easy culture and management, and its high sensitivity, we suggest d. exilis as a test organism adequate for toxicological studies in tropical and subtropical regions.